Investment Securities Textuals (Details) - USD ($)	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Investment Securities (Textual) [Abstract]
Cost, available-for-sale securities	$ 254,930,000,000		$ 249,653,000,000
Available-for-sale, at fair value	260,667,000,000		257,442,000,000
Held-to-maturity securities	80,102,000,000		55,483,000,000
Held-to-maturity, at fair value	80,315,000,000		56,359,000,000
Gross unrealized losses, investment securities	2,429,000,000		1,943,000,000
Fair value, investment securities	340,982,000,000		313,801,000,000
OTTI write-downs on held-to-maturity securities	0	$ 0
Collateralized debt obligations [Member]
Investment Securities (Textual) [Abstract]
Cost, available-for-sale securities	272,000,000		364,000,000
Available-for-sale, at fair value	407,000,000		500,000,000
Asset-backed Securities Collateralized by Auto Leases or Loans and Cash Reserves [Member]
Investment Securities (Textual) [Abstract]
Held-to-maturity securities	2,700,000,000		3,800,000,000
Held-to-maturity, at fair value	2,700,000,000		3,800,000,000
Asset-backed Securities Collateralized by Dealer Floorplan Loans [Member]
Investment Securities (Textual) [Abstract]
Held-to-maturity securities	1,600,000,000		1,900,000,000
Held-to-maturity, at fair value	1,600,000,000		2,000,000,000
Investment grade [Member]
Investment Securities (Textual) [Abstract]
Available-for-sale, at fair value	86,432,000,000		89,445,000,000
Held-to-maturity, at fair value	32,383,000,000		3,280,000,000
Gross unrealized losses, investment securities	2,213,000,000		1,697,000,000
Fair value, investment securities	118,815,000,000		92,725,000,000
Unrated investment grade securities [Member]
Investment Securities (Textual) [Abstract]
Gross unrealized losses, investment securities	24,000,000		25,000,000
Fair value, investment securities	$ 1,600,000,000		$ 1,600,000,000